Biodiversity is the variety of all living things found in a particular area. It captures how many different types of organisms exist and how they relate to one another. Scientists study biodiversity at three levels:
Genetic Diversity
The range of genetic variation within a single species. Greater genetic diversity helps populations adapt to changing conditions.
Species Diversity
The number of different species in an area and their relative abundance. This is the level most commonly measured in ecology.
Ecosystem Diversity
The variety of ecosystems found across a landscape or region, such as forests, wetlands, grasslands, and coral reefs.
Quantifying Species Diversity
To compare ecosystems, scientists need a way to assign a number to biodiversity. Simply counting species is not enough because it ignores how individuals are distributed among those species.
Simpson's Diversity Index solves this by accounting for both species richness (how many species are present) and evenness (how balanced the population sizes are across species).
The index produces a value between 0 and 1. A value closer to 1 indicates high diversity, while a value closer to 0 indicates low diversity, where one or two species dominate the community.
Diversity and Ecosystem Resilience
Ecosystems with higher biodiversity tend to be more stable and better equipped to withstand disturbances such as disease outbreaks, invasive species, or climate shifts.
When many species fill different roles in an ecosystem, the loss of one species is less likely to cause a collapse. Other species can compensate, maintaining the overall function of the community.
Understanding biodiversity helps scientists make informed decisions about conservation priorities, land management, and predicting how ecosystems will respond to environmental change.
The Formula
Simpson's Diversity Index is calculated using the following formula:
D = 1 - Σ(n/N)²
n = the number of individuals of each species N = the total number of all individuals in the community
For each species, you divide its count by the total, square the result, and sum those values. Subtracting from 1 gives the diversity index.
In this activity, you will compare two communities by calculating their Simpson's Diversity Index step by step.
Compare biodiversity between two ecological communities
Community A
1
Count Individuals
2
Calculate (n/N)²
Species
n
N
Your (n/N)²
3
Simpson's Index
✓
✓
Result
-
Community B
1
Count Individuals
2
Calculate (n/N)²
Species
n
N
Your (n/N)²
3
Simpson's Index
✓
✓
Result
-
Compare and Interpret
Great Job!
Simpson's Diversity Index: D = 1 - Σ(n/N)²
n = number of individuals of each species, N = total number of individuals